In the making of candles, the wax composition which may include both a fragrance and a color, is melted and poured into a mold in which it is allowed to cool. Characteristically, the mold is of aluminum and the wax cools and hardens by transfer of heat through the aluminum to the ambient air. The process is relatively slow, particularly where the candle is large in diameter, since most of the heat transfer takes place through the molded side wall of the candle.
Organic materials, in general, wax being no exception, have large coefficients of thermal expansion. Since the wax is customarily heated to a temperature of about 90.degree. C in the casting process, and the melting point is close to 70.degree. C, a considerable temperature drop must take place, as a result of which a considerable contraction must occur. However, since the mold is initially cold the wax which makes contact with the side wall of the mold solidifies first, and, therefore, forms a periphery which, in height, corresponds closely to the height at the time when the wax in contact with the side wall first solidifies. The wax in the interior of the candle, however, shrinks as it cools, the shrinkage continuing until solidification throughout the mass has taken place. The wax in immediate contact with the wick which is put in place before the wax is poured into the mold also establishes itself at a height which is approximately the same as that of the periphery of the candle.
The annular valley between the wick and the periphery of the candle is of such depth that the purchaser of such a candle feels that he has been treated unfairly in that the candle, for the most part, is not of the height attributed to it. Thus, a candle sold as a 6-inch candle is actually 6 inches high only at the periphery or at the center. Alternatively, the candle at these particular regions must be made substantially taller if the height of the candle at the low point of the valley is to be 6 inches. This, of course, represents a loss to the vendor in that the quantity of wax necessary for such a construction is increased above what would be the case if the candle were essentially flat at the top. Consequently, it would be highly desirable if a candle could be cast in such a way that the top would be essentially flat, or, at least, if the depth of the valley could be substantially decreased.
At the present time, the only means by which the difficulty can be avoided is to cast the candle in two or more stages. Thus, the valley or vortex must be filled in a second pouring in which some shrinkage, of course, also occurs. Consequently, it frequently happens that several pourings are necessary, especially where the candle is three or four times as great in height as in diameter.
Most commercial candles are colored; furthermore, most commercial candles have a fragrance incorporated. These ingredients have little or no effect on the depth of the vortex. Also, it is common to add stearic acid to the composition, the purpose being to provide the candle with a glossy exterior. Again, this ingredient does not affect the depth of the vortex.